(a) Field of the Invention
The present invention relates to a bonding method for a flexible film and a display device having a flexible film bonded by the bonding method.
(b) Description of Related Art
A liquid crystal display (LCD) includes (a) a lower panel having gate lines, data lines, switching elements, such as thin film transistors (TFTs), and pixel electrodes; (b) an upper panel facing the lower panel and having color filters and a common electrode; and (c) a liquid crystal (LC) layer interposed between the upper panel and the lower panel.
The switching elements, which receive both gate signals and data signals on the gate lines and the data lines, are activated by gate signals transmitted through the gate lines. The switching elements supply data voltages transmitted through the data lines to the pixel electrodes.
The gate lines are supplied with gate signals from a gate driver, and the data lines are supplied with data voltages from a data driver. The gate and data drivers include a plurality of integrated circuit (IC) chips which may be provided according to various types of assembly. The assembly is connected to the lower panel. In one type of assembly, the IC chips are mounted on the lower panel, and in another type of assembly, the IC chips are mounted on at least one flexible film. The former is called a COG (chip on glass) or a FOG (film on glass) assembly, and the latter is called a TCP (tape carrier package) assembly.
In the COG or FOG type assembly, the IC chips and the flexible film are directly mounted on the lower panel. The flexible film is called an FPC (flexible printed circuit), and it includes a flexible body, a plurality of signal lines formed on the body, and a protection film formed on the signal lines. The protection film for the FPC is formed with a cover layer, but it may be formed with a solder resist.
In the TCP type assembly, the IC chips are mounted on at least one flexible film attached to the lower panel. Under TCP type assembly, the assembly may be further classified into a TAB (tape automated bonding) type assembly or a COF (chip on film) type assembly. The TCP type assembly includes a flexible body, a plurality of signal lines formed on the body, a protection film formed on the signal lines, and IC chips mounted on the protection film. In this assembly type, the protection film is formed with a solder resist. The primary difference between flexible films of the TCP type assembly and flexible films of the COG or FOG type assembly is the mounting position of the IC chips.
A plurality of signals are generated at a controller mounted on a separate PCB (printed circuit board) and transmitted to the IC chips through the flexible film. The flexible film is attached to the lower panel using an anisotropic conductive film (ACF), which contains conductive particles that electrically connect the signal lines formed on the flexible film and the signal lines formed on the lower panel to each other.
However, when the flexible film is attached to the lower panel, a disconnection of the signal lines caused by external stress can occur at the bonding portions of the signal lines, which are not covered with a protection film.